Since SiC is thermally and chemically strong, and has good resistance to radiation, its commercialization as a device that can be used in harsh environments is expected. Moreover, SiC has a wide band gap, and it is easy to perform the control of p-type and n-type by doping an impurity, therefore making it useful as a visible light-emitting device material.
Though SiC as described above is a potential semiconductor material, its marketability is not sufficiently grown. One of the causes of this is the fact that crystal growth of SiC is difficult and production technique of a wafer with a large area is not established.
As a production method of crystal α-SiC, known conventionally are (1) Achison method, (2) a vapor epitaxial method, (3) a sublimation method, and (4) an improved sublimation method. In the Achison method cited as (1), a mixture of a silica stone and coke is heated at 2300° C. or more so that the crystal is deposited. The vapor epitaxial method cited as (2) is a CVD (Chemical Vapor Deposition) method, in which epitaxial growth is made on an α-SiC substrate in a temperature range of 1500° C. to 1800° C. The sublimation method of (3) is a method for sublimating SiC powder as a raw material in a graphite crucible and is deposited on a low temperature portion inside the crucible. Furthermore, the improved sublimation method of (4) is a method of placing an SiC substrate on a low temperature portion at an upper portion of the graphite crucible, and crystal SiC is grown on this substrate under Ar atmosphere.
As a method of producing the SiC wafer, the improved sublimation method of (4) is widely adopted for the reason of the SiC growth rate, the quality of the growth layer and the like.
However, in order to grow a crystal α-SiC with a large area with use of the above-described improved sublimation method, it is necessary to repeat growth of SiC with use of a small seed crystal made by the aforementioned Achison method to gradually grow it to the large area. This process requires tremendous time. Consequently, a production method of the α-SiC capable of producing a large amount with fewer process steps is desired. Moreover, machining the grown bulk SiC into a wafer shape requires cutting of SiC with high hardness by means of a diamond cutting grind stone and the like. This process makes it possible to obtain a single crystal of high quality, but it requires tremendous production cost.
The present invention has its object to provide the production method of an α-SiC wafer which solves the above-described disadvantages, and can produce a crystal α-SiC with stability and good reproducibility at low cost without using an expensive and hard-to-find seed crystal substrate.